Dot matrix printers may be of various diverse types, such as, helical printers and band printers. A dot-helix matrix printer, which is an enhancement of the bar-helix printer, consists of a rotating cylinder having rows of single raised dot print elements formed in a helical pattern around the peripheral surface. A plurality of print hammers having a bar-shaped impact surface is provided. A paper print medium is continuously fed between the hammers and the cylinder. Actuators are provided which selectively actuate the hammers to strike the dot print elements against an ink ribbon and paper whenever one of the dot elements is in position to be printed to record printed dots on the paper.
Band matrix printers employ a single set of raised dots distributed along a band or belt which moves horizontally across the paper to be printed. Another form is a drum printer which has raised dots distributed in columns around a drum which rotates around an axes parallel to the line to be printed. In both cases, printing is achieved by impacting the raised dot printing elements with a print hammer which results in the raised dots impacting a printing ribbon against paper and transferring ink or printing dots at the position of the dots when the paper is contacted. Patterns are printed by striking the hammers against the printing belt or drum whenever one of the dot printing elements, which move along the printing line, is in a position where a printed dot is desired. In this way, any desired pattern is formed by an array of dots which are printed along a line. Subsequent lines are printed by stepping the paper vertically or normal to the printing line.
It is well known that one limitation on the printing speed of impact printers such as impact line printers is the cycle time of the print hammer or maximum repetition rate of the pattern of the print elements on a dot-helix cylinder or on a belt, band or drum. It became apparent that it would be advantageous if the printer throughput could be improved for a given hammer repetition rate.